Generally speaking, coiling is more of a concern for loudspeaker cables than interconnects, but it is POSSIBLE to be a problem for either. In practice, the answer lies in the properties of the cables. If you coil up a single piece of wire, you will increase the inductance of the wire by concentrating the magnetic field. This increase in inductance reduces the accuracy of high current cables (such as speaker cable) and also increases the ability of the wire to pick up electromagnetic noise. So, if you had for example two completely separate conductors for the +/-, you would not want to coil a loudspeaker cable or an interconnect. However, most cables have both +/- run next to each other. This will somewhat contain the magnetic field through what is known as mutual inductance. If the inductance of the cable is low from a well contained magnetic field, coiling the cable should not have much impact. So, if the interconnect has a reasonably low inductance from reasonably close conductors, don't worry about it. (FYI if you have access to a meter that measures inductance, you can measure the cable inductance with and without coiling. If the inductance goes up with the coiling, it is better to avoid coiling.)
Regarding interconnect lengths, it is not recommended to run different lengths of cable if it can be avoided. If you believe that the cable is changing the signal running through it, then different length cables will obviously affect the signal differently. If on the other hand you believe that the signal is unaffected by the interconnects, then different lengths will not matter (of course if this was the case you probably would not be posting on an audiophile forum).
